The present invention relates to structured optical films and optical displays incorporating the structured optical films. More specifically, the present invention relates to a brightness enhancement film with reduced glancing angle output.
Electronic devices that include electronic displays for conveying information to a viewer have become nearly ubiquitous. Mobile phones, handheld computers, personal digital assistants, electronic games, car stereos and indicators, public displays, automated teller machines, in-store kiosks, home appliances, computer monitors, televisions, etc., are all examples of devices that include displays that people view on a daily basis.
The typical electronic display assembly contains a light source that is required in order for people to observe the information presented by the display. In battery powered equipment, the light source can represent a substantial fraction of the total power draw of the equipment. Therefore, reducing the amount of power required to produce a given luminance increases battery life, which is especially desirable in battery powered equipment.
Structured optical films are used in electronic display systems and in other applications where control over the direction of light, transmitted and/or reflected, is desired to increase brightness, reduce glare, etc. A structured optical film essentially comprises films of light transmissible materials in which a series of prisms are located such that the films can be used to redirect light through reflection and refraction. When used in an optical display such as that found in laptop computers, watches, etc., the structured optical film can increase brightness of an optical display by limiting light escaping from the display to within a pair of planes disposed at desired angles from a normal axis running through the optical display. As a result, light that would exit the display outside of the allowable range is reflected back into the display where a portion of it can be “recycled” and returned back to the structured film at an angle that allows it to escape from the display. That recycling is useful because it can reduce power consumption needed to provide a display with a desired level of brightness.
In conventional structured optical films, some light is allowed to exit the display outside the allowable range of angles relative to the normal axis running through the display. These high angle light rays may reduce the contrast of the display (the difference in brightness between light and dark areas of the display) and produce undesirable areas of brightness outside of a preferred viewing angle. It would be desirable to recycle these high angle light rays and return them back to the structured film for retransmission within the range of desired angles.